1. Field of Invention
The present invention relates to a defect inspection apparatus to be used for detecting defects of a circuit pattern formed on a surface of, e.g., a semiconductor device.
2. Related Background Art
Conventionally, a defect inspection apparatus has been used to detect the positions and sizes of defects of a circuit pattern formed on a surface of, e.g., a semiconductor device.
Referring to FIG. 25 showing a conventional defect inspection apparatus, a circuit pattern 2 formed on a surface 1a of a wafer 1 is to be detected and the wafer 1 is disposed on a XY-stage 3. The XY-stage 3 is constructed of a X-stage for shifting the wafer 1 in a x direction parallel to the paper of FIG. 25 within a two-dimensional plane and a Y-stage for shifting the wafer 1 in a y direction perpendicular to the paper of FIG. 25 within the two-dimensional plane.
A light source 4 such as a halogen lamp is disposed above the wafer 1. Light flux 5 emitted from the light source 4 is condensed by a collimeter lens 6 to be light flux 7, which then is incident on a beam splitter 8. Light flux 9 reflected by the beam splitter 8 illuminates a predetermined illumination area on the surface 1a of the wafer 1. Of light reflected from the surface 1a of the wafer 1, light flux 10 transmitted through the beam splitter 8 enters an imaging lens 11. The imaging lens 11 is disposed such that its object plane coincides with the surface 1a of the wafer 1 and an image of the circuit pattern on the wafer within the illumination area is formed on an image plane 12 of the imaging lens 11.
A two-dimensional image pick-up device 12 is provided to the image plane 12 such that its image pick-up surface coincides with the image plane 12. The image pick-up device 12 converts the image of the circuit pattern photoelectrically to obtain an image signal S1, which is output to a signal processor 14. In the meantime, a data storing section 15 supplies to the signal processor 14 a reference signal S2 corresponding to design data of a circuit pattern with no defect (nonerroneous circuit pattern). The signal processor 14 compares the image signal S1 with the reference signal S2 to obtain the presence or absence of defects of the circuit pattern on the surface 1a of the wafer 1, the sizes and positions of defects thereof. Defect information S3 of the circuit pattern is supplied from the signal processor 14 to a display 16, which displays the sizes and positions of defects of the circuit pattern on its screen.
In the above prior art, the processor 14 needs to perform a complex image processing at high speed so as to obtain the sizes and positions of the defects of the circuit pattern. Therefore, a high-speed computer is required as the signal processor 14 and the signal processing system becomes large.
For the purpose of solving this problem, there is another defect inspection apparatus in which a laser beam is converged on a small inspection area on the surface 1a of the wafer 1 without illuminating the large illumination area on the surface 1a of the wafer 1 and the wafer 1 is scanned linearly by the laser beam converged on the small illumination area by the use of an optical scanner (galvanomirror or the like) as an optical deflecting system. However, in the optical scanner, a mirror is oscillated to scan the laser beam, so that the inspection speed is limited owing to the upper limit of a scan rate and as a result, it takes a long time to inspect the entire surface of the wafer 1.